A urine culture is a test to find and
identify germs (usually bacteria) that may be causing a
urinary tract infection (UTI). Urine in the bladder
normally is sterile—it does not contain any bacteria or other organisms (such
fungi). But bacteria can enter the
urethra and cause an infection.
sample is kept under conditions that allow bacteria and other organisms to
grow. If few or no organisms grow, the test is negative. If organisms
grow in numbers large enough to indicate an infection, the culture is
positive. The type of organisms causing the infection are
identified with a microscope or by chemical tests.
infections are more common in women and girls than in men. This may be partly
because the female urethra is shorter and closer to the
anus, which allows bacteria from the intestines to
come into contact more easily with the urethra. (See a picture of the
female urinary tract.) Men also have an antibacterial substance in their
prostate gland that reduces their risk.
If the urine culture is positive, other tests may be done to help choose
which antibiotic will do the best job treating the infection. This is called
A urine culture may be done to:
You do not need to do anything before
you have this test. If you are taking or have recently taken
antibiotics, tell your doctor.
need to collect a urine sample. Avoid urinating just before having this
Talk to your doctor about any concerns you have regarding
the need for the test, its risks, how it will be done, or what the results will
mean. To help you understand the importance of this test, fill out the
medical test information form(What is a PDF document?).
You will be asked to collect a
clean-catch midstream urine sample for testing. The first urine of the day is
preferred because bacterial levels will be higher.
helps protect the urine sample from germs that are normally found on the penis
Collecting a urine sample does not cause
There is no chance for problems while collecting
a urine sample.
A urine culture is a test to detect and
identify organisms (usually bacteria) that may be causing a
urinary tract infection (UTI). Urine culture results
are usually ready in 1 to 3 days. Some organisms take longer to grow in the
culture; for this reason, results may not be available for several days.
No bacteria or other organisms (such as
fungi) grow in the culture. The culture result is
Organisms (usually bacteria) grow in the
culture. The culture result is positive.
count of 100,000 or more bacteria per
milliliter (mL) of urine may be caused by an
infection. A count ranging from 100 to 100,000 could be either caused by
infection or by contamination of the sample (you may need a repeat urine
culture). If the count is 100 or less, infection is unlikely; however, a count
of 100 or less may also be seen if you are already taking
If test results are positive,
sensitivity testing may be done to help make decisions
Reasons you may not be able to
have the test or why the results may not be helpful include:
Other Works ConsultedChernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis:
Saunders.Fischbach FT, Dunning MB III, eds. (2009).
Manual of Laboratory and Diagnostic Tests, 8th ed.
Philadelphia: Lippincott Williams and Wilkins.Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.
May 21, 2012
E. Gregory Thompson, MD - Internal Medicine & W. David Colby IV, MSc, MD, FRCPC - Infectious Disease
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